Hash Table of Vectors of Person Objects c - c++

Question

I've been working on a very in depth project for one of my classes. It supposed to read in Person objects and put them into a hash table. I'm still trying to get my head around the concept of a hash table so any help would be appreciated.
It will be hashing based on last name and since some people may have the same last name, I was going to make each bucket a vector of Person objects. I'm trying to test the class by adding a person to the hash function and then returning it. My code compiles successfully but I get a thread error in the put function on this line: table[index].push_back(p);
Could anyone please help me figure out what is going wrong? Thank you!
int main()
{
HashTable ht(10);
ht.put(p1, p1->lName);
ht.getName("Booras");
}
HashTable:
#include "Person.h"
#include <vector>
class HashTable: public DataStructures
{
private:
vector<vector<Person>> table;
public:
HashTable(int tableSize);
~HashTable();
int tableSize;
void getName(string str); //prints out friends with matching name
void put(Person p, string str);
void remove(Person *p, string str);
int hash(string str);
};
HashTable::HashTable(int tableSize)
{
vector< vector<Person> > table(tableSize, vector<Person>(tableSize));
for (int i = 0; i < tableSize; i++) {
table.push_back(vector<Person>()); // Add an empty row
}
}
HashTable::~HashTable()
{
}
//Find a person with the given last name
void HashTable::getName(string key)
{
int index = hash(key);
for(int i=0; i<table[index].size(); i++)
{
if(table[index][i].lName.compare(key) == 0)
std::cout << "Bucket: " << index << "Bin: " << i;
table[index][i].print();
}
//create exception for person not found
}
void HashTable::put(Person p, string str)
{
int index = hash(str);
table[index].push_back(p);
}
void HashTable::remove(Person *p, string str)
{
int index = hash(str);
int i=0;
while(&table[index][i] != p && i<table[index].size())
i++;
for(int j=i; j<table[index].size()-1; j++)
table[index][j] = table[index][j+1];
table[index].pop_back();
}
int HashTable::hash(string str)
{
int hashValue = 0;
for(int i=0; i<str.length(); i++)
{
hashValue = hashValue + int(str[i]);
}
hashValue %= tableSize;
if(hashValue<0) hashValue += tableSize;
return hashValue;
}
Main:
int main() {
Person *p1 = new Person("Kristy", "Booras", "Reston", "03/15");
HashTable ht(10);
ht.put(*p1, p1->lName);
ht.get("Booras");
return 0;
}

Answer 1

You don't show us the HashTable::hash(string) member function, but I'd assume that your problems originate in the HashTableconstructor: You don't initialize the tableSize member variable, which you'll need to calculate a valid hashed index.
While looking at the constructor:
HashTable::HashTable(int tableSize)
{
vector< vector<Person> > table(tableSize, vector<Person>(tableSize));
This has initialized table to have tableSize non-empty elements, for a total of tableSize * tableSizedefault-constructed Person objects.
for (int i = 0; i < tableSize; i++) {
table.push_back(vector<Person>()); // Add an empty row
}
}
Now you have added more rows, so that table.size() == 2*tableSize, with the first half of entries non-empty (as explained above) and the second half holding empty vectors.
That is probably not what you intended.
And in all of that you haven't initialized the member tableSize. It easily gets confusing, if you use local variables or argument names that hide member names.